1. Field of the Invention
The present invention relates to an apparatus and a method for fabricating a light guide panel of a liquid crystal display, and more particularly to an apparatus and a method for fabricating a light guide panel which are capable of reducing the thickness of a stamper and of firmly fixing the stamper.
2. Description of the Related Art
In general, a liquid crystal display (hereinafter referred to as “LCD”) displays pictures on a screen by controlling the transmittance of light beams supplied from a back light unit. The controlling function is performed by a liquid crystal display panel that has a plurality of liquid crystal cells arranged in a matrix and a plurality of control switches for switching video signals to be supplied to each liquid crystal cell.
FIG. 1 illustrates the structure of a related art back light unit for use in a conventional LCD. Referring to FIG. 1, the related art back light unit includes: a lamp 10 for generating light beams; a lamp housing 14 for accommodating the lamp 10; a light guide panel 12 for transforming the light beams incident from the lamp 10 into a surface light source; optical sheets 18, 20, 22, and 24 attached on the light guide panel 12 and for increasing the efficiency of light incident to a liquid crystal display panel (not shown); and a reflection plate 16 which is placed under the light guide panel 12 and reflects the light beams coming from the rear surface of the light guide panel 12 toward the liquid crystal display panel. Also, the liquid crystal display panel is placed above the back light unit and displays pictures on a screen by controlling the transmittance of light beams supplied from the back light unit.
The lamp 10 is commonly a cold cathode fluorescent lamp. The light beams generated by the lamp 10 reach the light guide panel via the incident surface present at one side of the light guide panel.
The lamp housing 14 is installed to accommodate the lamp 10, and has inner reflecting surfaces to reflect the light from the lamp 10 toward the incident surface of the light guide panel 12.
The light guide panel 12 transforms the light beams incident from the lamp 10 into a surface light source. This light guide panel 12 has a sloped rear surface and a planar exit surface, and is fabricated so as to make the incident surface perpendicular to the exit surface. The reflection plate 16 is placed under the light guide panel 12 so as to face the rear surface thereof. The light guide panel 12 causes the lights incident from the lamp 10 to reach regions far from the lamp 10. The light guide panel 12 is generally fabricated from polymethylmethacrylate (PMMA), which has high degree of strength so that it cannot be easily deformed or broken, and which has a high transmittance of light.
The reflection plate 16 re-reflects the light incident through the rear surface of the light guide panel 12 toward the light guide panel 12, and reduces the loss of light. When the light from the lamp 10 comes to the light guide panel 12, it is reflected at an angle of reflection by the sloped rear surface and is directed toward the exit surface. Here, the light coming to the rear surface and sides of the light guide panel 12 are reflected by the reflection plate 16 and then go toward the exit surface. The diffusion sheet 18 diffuses the light beams coming via the exit surface of the light guide panel 12 over the entire space of the back light unit.
On the other hand, the efficiency of light becomes high when the light incident to the liquid crystal display panel is perpendicular thereto. To do this, two prism sheets 20 and 22 are stacked to make the light coming from the light guide panel 12 go toward the liquid crystal display panel at a incident angle of 90-degrees. The first and second prism sheets 20 and 22 are shaped in a plurality of prism bars having hills and valleys. The two prism sheets 20 and 22 collect the light beams coming from the diffusion sheet 18 and cause them to go toward a screen with a right angle incident angle.
A protection film 24 is used to protect the surface of the second prism sheet 22, and also to diffuse the light to make its distribution uniform.
On the other hand, in order to enhance the lighting efficiency the light guide panel 12 has patterns on at least one of the rear surface and the exit surface. Fabricating apparatuses illustrated in FIGS. 2 to 4 are used to form these patterns on the light guide panel 12.
The apparatus for fabricating the light guide panel illustrated in FIG. 2 includes: an upper mold frame 32 for forming patterns on the exit surface of the light guide panel 12; a side mold frame 40; a lower mold frame 34 for forming patterns on the rear surface of the light guide panel 12, wherein the upper, side, and lower mold frames 32, 40 and 34 together form a set of injection molding frames; and a first and a second fixing parts 36 and 38 for fixing externally the upper, side, and lower mold frames 32, 40, and 34. Light guiding patterns (not shown) for enhancing the optical performance of the light guide panel 12 are formed on at least one of the upper and lower mold frames 32 and 34. These light guiding patterns are directly formed on at least one of the upper and lower mold frames 32 and 34 through a cutting or corrosion process. However, there is a problem that the light guiding patterns that are formed on at least one of the upper and lower mold frames 32 and 34 are not uniform. Also, there is another problem wherein when making the light guide panel, the fabrication of the upper and lower mold frames and the formation of the light guiding patterns requires several days. To solve these problems, the fabricating apparatus illustrated in FIG. 3 is used.
The fabricating apparatus illustrated in FIG. 3 includes: a stamper 46 attached to the upper mold frame 32 to form radiating patterns on the exit surface of the light guide panel 12; an air induction pipe for attaching the stamper 46 to the upper mold frame 46 using air suction force; and a stamper fixing piece 42 located at one side of the upper mold frame 32 for determining the position of the stamper 46. The stamper 46 has light guiding patterns (not shown) formed thereon that define the radiating patterns on the exit surface of the light guide panel. The lower mold frame 34 has light guiding patterns (not shown) formed thereon that define rear patterns on the rear surface of the light guide panel through the cutting or corrosion process. While the fabricating apparatus for the light guide panel using this stamper 46 makes it possible to reduce the fabrication time for the light guide panel by attaching the stamper 46 to the upper mold frame 32, there is a problem that the stamper 46 cannot be assembled with the lower mold frame 34. If the stamper is to be assembled with the lower mold frame 34, an additional air induction pipe 44 for fixing the stamper 46 results in a more complex fabricating apparatus for the light guide panel. To solve these problems, the fabricating apparatus for the light guide panel illustrated in FIG. 4 is used.
The fabricating apparatus for the light guide panel illustrated in FIG. 4 includes a lower stamper 28 coupled with the lower mold frame 34 through screws 48. The lower stamper 28 and an upper stamper 46 attached to the upper mold frame 32 have the light guiding patterns for defining the rear patterns and radiating patterns respectively on the light guide panel. To be coupled with the lower mold frame 34 without the air induction pipe, the lower stamper 28 is fixed through screws 48 and formed having a thickness in the range 4-8 mm.
To be fixed without the air induction pipe, the lower stamper 28 of the fabricating apparatus illustrated in FIG. 4 is formed to be relatively thick. In this case, there are problems in that it is difficult to make the lower stamper 28 thin, requiring a longer fabricating time to form the light guiding patterns of the lower stamper 28.